I’ll try running it myself to reproduce the error and document the steps to get it working, but one of the key causes for not staying up is if Java (or the jar) exit immediately.
Is the server pack you’re running have all the required accompanying jars, e.g., the forge installer.jar was run and it downloaded the appropriate forge dependencies?
Can you provide the relevant logs that indicate the server started (because it definitely seems to)?–it will probably indicate what Java/Forge related issue closed the process.